From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-5.5 required=3.0 tests=BAYES_00, HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS, URIBL_BLOCKED,USER_AGENT_SANE_1 autolearn=no autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id 55A51C433EB for ; Tue, 14 Jul 2020 19:10:17 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 35F6B2064C for ; Tue, 14 Jul 2020 19:10:17 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1730688AbgGNTKH (ORCPT ); Tue, 14 Jul 2020 15:10:07 -0400 Received: from mga09.intel.com ([134.134.136.24]:65171 "EHLO mga09.intel.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1730189AbgGNTJw (ORCPT ); Tue, 14 Jul 2020 15:09:52 -0400 IronPort-SDR: 9Bfeb0/0Naw0dTcYqAOMzBFQIbwFhqES6uIjGLDuwYS6ZDA9k7rTiIx6IdmO+QnHqP7wxi5UuR 3y9gI5QUBFDA== X-IronPort-AV: E=McAfee;i="6000,8403,9682"; a="150426923" X-IronPort-AV: E=Sophos;i="5.75,352,1589266800"; d="scan'208";a="150426923" X-Amp-Result: SKIPPED(no attachment in message) X-Amp-File-Uploaded: False Received: from orsmga006.jf.intel.com ([10.7.209.51]) by orsmga102.jf.intel.com with ESMTP/TLS/ECDHE-RSA-AES256-GCM-SHA384; 14 Jul 2020 12:09:46 -0700 IronPort-SDR: F5+6TagJ+l1griOYsZtzQkFGRpSQRa2AcrvfdSOx4vFmi7tumHZNFRIJUHlFtNvtasUh0ZpCV3 s3kdDTQFO7MA== X-ExtLoop1: 1 X-IronPort-AV: E=Sophos;i="5.75,352,1589266800"; d="scan'208";a="285855453" Received: from iweiny-desk2.sc.intel.com ([10.3.52.147]) by orsmga006.jf.intel.com with ESMTP; 14 Jul 2020 12:09:45 -0700 Date: Tue, 14 Jul 2020 12:09:45 -0700 From: Ira Weiny To: Peter Zijlstra Cc: Thomas Gleixner , Ingo Molnar , Borislav Petkov , Andy Lutomirski , Fenghua Yu , x86@kernel.org, Dave Hansen , Dan Williams , Vishal Verma , Andrew Morton , linux-doc@vger.kernel.org, linux-kernel@vger.kernel.org, linux-nvdimm@lists.01.org, linux-fsdevel@vger.kernel.org, linux-mm@kvack.org, linux-kselftest@vger.kernel.org Subject: Re: [RFC PATCH 04/15] x86/pks: Preserve the PKRS MSR on context switch Message-ID: <20200714190945.GD3008823@iweiny-DESK2.sc.intel.com> References: <20200714070220.3500839-1-ira.weiny@intel.com> <20200714070220.3500839-5-ira.weiny@intel.com> <20200714082701.GO10769@hirez.programming.kicks-ass.net> <20200714185322.GB3008823@iweiny-DESK2.sc.intel.com> <20200714190539.GG5523@worktop.programming.kicks-ass.net> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20200714190539.GG5523@worktop.programming.kicks-ass.net> User-Agent: Mutt/1.11.1 (2018-12-01) Sender: linux-fsdevel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-fsdevel@vger.kernel.org On Tue, Jul 14, 2020 at 09:05:39PM +0200, Peter Zijlstra wrote: > On Tue, Jul 14, 2020 at 11:53:22AM -0700, Ira Weiny wrote: > > On Tue, Jul 14, 2020 at 10:27:01AM +0200, Peter Zijlstra wrote: > > > On Tue, Jul 14, 2020 at 12:02:09AM -0700, ira.weiny@intel.com wrote: > > > > From: Ira Weiny > > > > > > > > The PKRS MSR is defined as a per-core register. This isolates memory > > > > access by CPU. Unfortunately, the MSR is not preserved by XSAVE. > > > > Therefore, We must preserve the protections for individual tasks even if > > > > they are context switched out and placed on another cpu later. > > > > > > This is a contradiction and utter trainwreck. > > > > I don't understand where there is a contradiction? Perhaps I should have said > > the MSR is not XSAVE managed vs 'preserved'? > > You're stating the MSR is per-*CORE*, and then continue to talk about > per-task state. > > We've had a bunch of MSRs have exactly that problem recently, and it's > not fun. We're not going to do that again. Ah sorry, my mistake yes I meant 'per-logical-processor' like Dave said. I'll update the commit message. Ira